Thermionic relay circuits



Aug. 23, 1938. A. H. LAMB THERMIONIG RELAY CIRCUITS Filed sept. 1, 1955 Patented Aug. 23, 1938 UNITED .STATES PATENT OFF-ICE THEBMIONIC RELAY CIRCUITS Application September "I, 1935, Serial No. 39,654

' 11 Claims.

This invention relates to thermionic relay circuits and more particularly to circuits in which the space current path of the relay circuit lies in a flame stream.

It has been proposed to control the operation of electronic tubes, such as grid glow tubes and amplifiers, by changes in the conductivity of a flame. The grid bias circuits of the electronic tubes included a source of polarizing potential and a portion of the flame path and, in general, the action was exactly the same as that which would take place if a mechanical resistor of variable magnitude were substituted for the resistance of the flame path. In these prior control systems, the initial or primary control circuit is of the voltage-change type, and the voltage change resulting from a variation in the resistance of the flame path is employed to control the electronic tube. The ultimate control is obtained by the action of a current-change device or relay in the output circuit of the tube.

An object of the present invention is to provide a relay circuit including, in series, the thermionic or space current path of an open flame and a current-responsive control device. An object is to provide a flame-controlled relay circuit of simple electrical and physical design that may be energized from the usual house lighting circuits of either the alternating or direct current type. More particularly, an object is to provide a relay circuit including a current-responsive control device and a source of voltage in series with two electrodes, the electrodes being spaced apart in a flame stream and only one 35 of theelectrodes being an electron-emitting body energized by the heat of the flame.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 is a schematic diagram of an embodiment of the invention;

Fig. 2 is a fragmentary diagram illustrating another arrangement of the electrodes with respect to the flame path;

Fig. 3 is a circuit diagram of an embodiment of the invention as applied to a safety control for a fuel burner; and

Fig. 4 is a chart showing the relation between voltage and current when operating the invention from an alternating current source.

In the drawing, the reference numeral l identifles a nozzle for projecting a flame stream 2 in which an electron-emitting electrode 3, such as a wire of tungsten or a nickel-chromium alloy, is

positioned. As shown in Fig. 1, the nozzle l acts as the cooperating electron-receiving electrode or anode when maintained at a positive potential with respect to electrode 3 by a current source 4. The moving coil 5 of a sensitive current-responsive relay is included in the circuit between the electrodes, the relay being preferably of the type including a movable arm 6 carrying a magnetic rider 1 for cooperating with a relatively stationary contact 8 in the form of a small permanent magnet. Magnetic attraction at the contacts assures good contact engagements, and a pusher arm 9 is provided for separating the contacts. The pusher arm maybe operated manually by a knob 9'.

The exact design of the sensitive instrument type relay is not an essential feature of this invention, and appropriate constructions of the magnetic contact type are illustrated and. claimed in my prior patents numbered 2,014,385 to 2,014,388, inclusive, granted Sept. 17, 1935. While this is the preferred construction, it is possible to use sensitive relays of the presser bar type in some instances.

The circuit controlled by the sensitive relay includes a source of current [0 and an alarm or control unit ll serially connected between the contact arm 6 and the magnetic contact 8. So long as the thermionic current established by source 4 between the electrodes I and 3 remains above some predetermined value, the current flow in the moving coil 5 prevents an engagement of the relay contacts I, 8. The thermionic current ceases when the flame is extinguished, and the contacts 1, 8 engage to energize the signal or control device II.

It is particularly to be noted that the ohmic resistance between electrodes l and 3 has a negligible effect upon the operation of this thermionic relay system. The resistance between the electrodes is reduced when the flame is present, but the current flow which determines the operation of the relay is a thermionic current between the electron-emitting electrode or cathode 3 and the cold electrode or anode I. that the purely conductive current flow between the electrodes is of an order substantially lower than that of the thermionic current, and not suflicient to operate the relay system, may be demonstrated by reversing the polarity of the 0 The fact 4 tion, the cold electrode or anode I2 is not located in, but adjacent to, the flame stream 2. The gap between the flame stream and the anode I! may be of the order of inch when the potential of the current source 4 is as low as about 110 volts.

Relays such as contemplated by this invention may be used for various purposes where a control or an alarm device is to be actuated upon the presence, or the absence, of a flame stream. The invention is well adapted for use as a safety control for, oil burners and/or in other heaters employing a pilot flame.

A typical form of safety control for an oil burner is illustrated in Fig. 3. The nozzle l directs the pilot flame 2 into the path of the fuel projected from the burner nozzle IS. The control system for the main burner may be of any appropriate or desired design, as is indicated by the block element II which is energized from an appropriate power source i5 which, in most instances, is the usual 110 volt power line. Leads I 6, l6 extending from the block element I! to the contact arm 6 and magnetic contact 8, respectively, of the sensitive relay indicate the operation of the burner control is dependent upon an open circuit between the relay contacts.

It is not essential that a direct current source of potential be included in the relay system and, as shown in Fig. 3, an alternating current source 4' is employed. This current source may be, and preferably is, the usual 110 volt system for house lighting. Commercial power systems are either 25 or 60 cycle and the damping of the moving system of the relay must be such that it will not respond to frequencies of this order.

The operation of the burner control will be apparent from a consideration of the curves oi. Fig. 4. The voltage on the cold electrode or anode l varies periodically from 110 volts positive to 110 volts negative, as indicated by the curve IT. The current flow between electrodes l and 3 includes an alternating current component, shown by curve II, which is relatively small, for example of the order of a fraction of a microampere. It is to be noted that the prior voltage-change control systems, as noted above, employed this conductive current component to obtain a control action and transformers were used to produce high bias voltages, of the order 01' 400 to 600 volts, to produce the required grid bias variation by the relatively high conductivity of a flame stream. According to this invention, the conductive current is not employed to produce a change in the biasing potential applied to a thermionic tube but a thermionic current of much greater value is established at a lower potential difference and flows through a current responsive device to actuate the same. The thermionic current is extinguished during half-cycles when the cold electrode I is negative, but rises to values of the order of 20 microamperes when the cold electrode is at a positive potential with respect to the electron-emitting electrode 3. The rectifier action thus results in periodic current impulses, indicated by curves IQ, of a magnitude adequate for the actuation of a relay instrument oi. high sensitivity. As noted above, the damping of the moving coil system must be such that it does not respond to the frequency oi. the alternatingcurrent source but to the average value of the pulsating current. In general, the damping is preferably such that the moving system will not respond to frequencies about 2 or 3 cycles per second and, in the case of oil burners which may roar and burn unevenly, it may be desirable to increase the damping to prevent the relay from responding to current fluctuations of one cycle per second. thus preventing the relay from closing in response to momentary current drops due to the uneven flame or combustion.

It will be apparent that the invention is not limited to the particular embodiments herein illustrated and described. The design of the controlled circuit may be varied in accordance with the particular control which is required in any given installation. The relay may be, for example, of the type described in my prior Patent No. 2,014,386 and include means for operating a control switch only upon a predetermined number of closures of the relay contacts. Such a relay is especially suited for use in an oil burner control in which the oil burner is to be tie-energized only upon a failure to establish a flame by a predetermined number of trials. The invention is not restricted in its applications to a safety control for oil furnaces, but may be used in flre alarms or for indicating or controlling abnormal conditions in a furnace or other heating systems. The invention is therefore open to substantial variation in the design and relation of the several components of a thermionic control or signal system.

I claim:

1. In a thermionic relay circuit, means for establishing a flame stream, an electrode normally heated to electron-emitting temperature by the flame stream, a second electrode for receiving electrons emitted by the first electrode, said second electrode being heated by the flame stream to a substantially lesser degree of electron emission than the first electrode and a source of potential and a current-responsive control device serially connected between said electrodes to complete a circuit in which a thermionic current is produced by the attraction of electrons to said second electrode when that electrode has a positive potential with respect to the first electrode, said control device including a pair of contacts and movable means actuated by thermionic current flow in said circuit for controlling said contacts.

2. A thermionic relay circuit as claimed in claim 1, wherein said source of potential is an alternating current source.

3. A thermionic relay circuit as claimed in claim 1, wherein said source of potential is an alternating current source, and said means of the control device is damped to render the same non-responsive to current impulses of the frequency of the alternating current source of potential.

4. In a relay circuit, the combination with means for establishing a flame stream, of an electrode positioned to be heated to electronemitting condition by said flame stream, a cooperating relatively cold electrode, a sensitive relay instrument comprising a moving coil carrying a contact cooperating with a relatively stationary contact, a source oi. potential, and means connecting the moving coil and the source of potential in series between said electrodes.

5. A relay circuit as claimed in claim 4, wherein said means for establishing a flame stream constitutes said cooperating electrode.

6. A relay circuit as claimed in claim 4, wherein said source of potential is an alternating current source.

7. A relay circuit as claimed in claim 4,

' relay having a moving system actuating one of a pair of contacts in a controlled circuit, an electron-emitting electrode, an anode, and a source of polarizing potential connected in series with said moving system between said electrode andanode, characterized by the fact that said electrode is positioned to be heated to electronemitting temperature by a flame stream and said anode is heated by the flame stream to less than electron-emitting temperature.

9. A thermionic relay of the type including a source of polarizing potential and a relay device serially connected between a cathode and an anode, said relay device including relatively movablecontacts adapted to be included in a controlled circuit, characterized by the fact that said cathode and anode are positioned at spaced points in open air to be heated by a flame, and said cathode is heated to electron-emitting temperature by the flame.

10. In a relay device, the combination with a circuit to be controlled and including a par of relatively movable contacts, of a pair of electrodes spaced apart in open air, one electrode being adapted to emit electrons when heated, a source of potential for establishing a thermionic current between said electrodes when said electron-emitting electrode is heated, and means responsive to the thermionic current for effecting relative movement of said contacts, said means being connected in series with said potential source and said electrodes.

'11. Apparatus controlled by a combustion flame, including: an electrode having an appreciable portion located in the flame and heated thereby to emit electrons, a second electrode adjacent said flame but sufliciently spaced therefrom to remain at a temperature below that at which it emits electrons; means for maintaining between said electrodes a voltage diiierential of a magnitude to establish a thermionic current flow between said electrodes while said portion in said flame is heated thereby; and'current responsive means in series with said electrodes.

ANTHONY H. LAMB. 25 

